1. Field
The present invention relates to a direct synthesis method of a nanostructured catalyst particles on various supports and a catalyst structure produced by the same.
2. Description of the Related Art
In every technical field in which catalysts are used, it is quite important to address challenges in improving performance of high priced platinum (Pt) based catalysts or replacing the high priced Pt based catalysts with price-competitive catalysts.
In particular, in technical fields, in which catalysts for electrochemical reactions are required, such as an oxygen reduction reaction (ORR) for oxygen reduction in a fuel cell system, a reduction-oxygen (REDOX) couple reaction in a reverse electrodialysis system, a cathodic hydrogen evolution reaction, a water oxidation reaction, and the like, it is urgently demanded to reduce the costs of conventional expensive Pt based catalysts or to develop catalysts for replacing the conventional catalysts.
Since only exposed atoms of most metal catalysts are involved in reactions, it is possible to reduce the amount of expensive metals used. In addition, since metals are readily sintered due to poor thermal stability, metal catalysts may suppress catalytic activity from being lowered. Further, since use of only metals makes it difficult to achieve an appropriate level of mechanical strength, metal catalysts dispersed in a carbon based support or a non-carbon based support may be used.
An electroless method as one of the most traditional methods, in which a catalyst is generally coated on a support, was proposed by Ki Chul Park et al. in an article “Carbon-supported Pt—Ru nanoparticles prepared in glyoxylate-reduction system promoting precursor-support interaction, Journal of Materials Chemistry, 2010, 20, 5545-5556. According to the proposed method, however, many steps should be performed, which is quite burdensome. In addition, it is necessary to use different kinds of reducing agents according to the kind of support used. Moreover, it is difficult to control a particle size to 2 nm or less, and it is also difficult to achieve uniform distribution of particles and an increased dispersion density.
A method of controlling a catalyst structure, which is very advantageous in synthesizing heterostructures, such as core-shell structures, was proposed by Dan Chen, et al. in a report “Ultra-high-performance core shell structured Ru@Pt/C catalyst prepared by a facile pulse electrochemical deposition method,” Scientific Reports, 2015, 5, 11624. This method is advantageous in that the process is simplified and can be performed at room temperature. According to this method, however, it is difficult to produce the catalyst structure in large scales and to control a particle size of the catalyst structure to 2 nm or less, and it is also difficult to achieve uniform distribution of particles and an increased dispersion density. In addition, it is quite difficult to hold catalyst particles in a powder-type support.
A chemical vapor deposition (CVD) method is described in a literature entitled “Chemical Vapor Deposition (CVD) of Iridium, Platinum, Rhodium and Palladium,” by J. R. Vargas Garcia et al., Materials Transactions, 2003, 44, 1717-1728. An atomic layer deposition method is described in an article entitled “A highly active, stable and synergistic Pt nanoparticles/Mo2C nanotube catalyst by atomic layer deposition (ALD) for methanol electro-oxidation, K Zhang et al., NPG Asia Materials, 2015, 7, e155. A method of synthesizing nano-sized catalysts on support surfaces while supplying molecules generated by evaporating a precursor containing a metal or an organic material useful as a catalyst in a wide sense at room temperature or low temperatures into a reactor is described in a report entitled “Green synthesis of carbon-supported nanoparticle catalysts by physical vapor deposition (PVD) on soluble powder supports” by H. Y. Park et al., Scientific Reports, 2015, 5, 1424. According to the above-described methods, uniform synthesis and controlling are easily achieved in a case where supports in the form of powder are used. However, in a case where supports are used in large quantities, the catalyst may not be uniformly coated, making it disadvantageous to be employed in coating a powder-type catalyst. Above all, this method is disadvantageous in that there is a considerable loss of precursor sources, lowering economic efficiency.
A microwave assisted polyol method for the preparation of Pt/C, Ru/C and PtRu/C nanoparticles and its application in electrooxidation of methanol were proposed by Srinivasan Harish et al. According to the proposed method, a metal salt material is used as a catalyst source and the nanoparticles are prepared at relatively low temperatures in the range of approximately 100° C. to approximately 200° C. for 10 minutes, thereby minimizing the synthesis cost and time. However, it is not easy to synthesize the catalyst to have a particle size of 2 nm or less, and it is difficult to achieve uniform distribution of particles and an increased dispersion density. In addition, mass production of catalysts in kilogram scales is quite difficult to achieve, resulting in poor economical efficiency.